Showing papers by "Vadim V. Silberschmidt published in 2007"

Effect of Impact-Fatigue on Damage in Adhesive Joints

Abstract: In recent decades the use of structural adhesive joints in the aerospace industry has increased considerably thanks to their high strength-to-weight ratio, low stress concentration and capacity to join different adherends. There is increasing interest in damage due to low-velocity impacts produced in adhesively bonded components and structures by vibrating loads. This type of loading is known as impact fatigue. The main aim of this paper is to investigate damage evolution in adhesive joints subjected to impact-fatigue and to compare this with damage evolution in standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). In this work, adhesively bonded lap joints were subjected to multiple tensile impacts tensile and it was seen that this type of loading was extremely damaging compared to standard fatigue. A number of methods of studying damage evolution in bonded joints subjected to fatigue and impact fatigue loading have been investigated and various parameters have been used to characterise these processes. Two modifications of the accumulated time-stress model [1-4] are proposed and it is shown that both models provide a suitable characterization of impact-fatigue in bonded joints.

Propagation of delamination zones in bonded joints

Abstract: Delamination is one of the main failure mechanisms in bonded composite joints. Owing to a considerable spatial scatte r in adhesion over the interface in such joints, initiation of a delamination zone and propagation of its front are highly random processes. The main delamina- tion front is rather tortuous, and many small delamination spots are formed in its immediate vicinity. These processes can be additionally complicated in the case of loading types such as fatigue and/or multiple impacting. This paper deals with experimental methods of analysing delamination zones at various stages of their ev olution. X-radiographs of delamination zones are digitalized and scaling analyses based on fractal a nd multifractal approaches are performed in order to quantify the morphology as well as the damage distribution in the immediate vicinity of delamination fronts.

Crystallographic Structure and Mechanical Behaviour of SnAgCu Solder Interconnects under a Constant Loading Rate

Abstract: With the continuing increase of the integration density in electronics, dimensions of interconnections for electronic components have been miniaturized to a scale that is comparable to those of their crystallographic structure. For instance, a SnAgCu solder joint in the flip chip package can contain only one or a few grains. In this case, the mechanical behaviour of the micro-joint is expected to shift from a polycrystalline-based to single-crystal one. Considering the further miniaturization, both the crystallographic structure and mechanics of each component (Ag3Sn, Cu6Sn5 and beta-Sn matrix) within a grain and the adjacent SnCu interface will play an important role in the reliability of the micro-joint due to their size comparable with that of a grain, irregular geometry, their heterogeneous distribution and considerably different properties. In addition, at such a small scale, the non-local effect on deformation of beta-Sn should be taken into account to interpret mechanical interactions between components. In this paper, a shearing test, in which it is possible to apply a constant loading to a SnAgCu joint is deigned to investigate mechanics of substructure within a SnAgCu grain and near the SnCu interface.

Creep Analysis of a Lead-free Surface Mount Device

Abstract: In this paper finite element analysis (FEA) is used to understand the effect of a non-uniform temperature distribution on the creep and fatigue behaviour of lead-free solder joints in an electronic assembly comprising of a chip resistor mounted on printed circuit board (PCB). Solder joints in surface mount devices (SMDs) operate over a temperature range as extreme as -55degC to 125degC, which is high compared to the melting temperature of solder alloys. Exposure of solder joints to these temperatures can result in thermo-mechanical fatigue. Eutectic or near- eutectic tin-lead alloys have previously been used as an interconnection material, but the ban imposed on the use of toxic materials in electronic products demands new lead-free solder materials. This paper presents the experiments carried out using a thermal camera to obtain the real temperature distribution in the electronic assembly. These temperature distributions were used in FEA of the chip resistor under temperature cycling conditions. Unlike accelerated tests for obtaining reliability data, FEA is quick and less expensive.